In fabricating a force or pressure sensor array, conventionally, a strain gauge is configured using a Ni/Cr or Cu/Ni metal layer. However, this method is disadvantageous in that since a gauge factor is lower than that of a semiconductor strain gauge as much as 50 to 100 times, sensitivity is lowered as much.
The semiconductor strain gauge is fabricated by injecting impurities into mono-crystalline or polycrystalline silicon, and since the gauge factor is considerably high as much as 150, the semiconductor strain gauge has a high-sensitive sensing capability. However, due to lack of flexibility and problems of conventional fabricating processes that cannot be done together with like a polymer-based fabricating process, its application to a flexible and bendable force or pressure sensing array is limited.
On the other hand, a force or pressure sensor array has been constructed using a force- or pressure-sensitive conductive rubber or ink layer, which is a mixture produced by blending conductive tiny metal powder using rubber or polymer as a base material. If power or pressure is applied, the base material is deformed, and the distance among the particles of the metal powder in the rubber or ink layer is narrowed, or the particles are contacted with one another. Accordingly, a path for flowing electricity is created, and thus resistance is reduced. Since a large-area sensor array can be fabricated at a low cost, the sensor array is already widely used as an element for measuring distribution of pressure for medical or ergonomic purposes. However, since the characteristics of the sensor array depend on conductivity of the metal particles scattered in the base material, repeatability and restorability are significantly lowered, and thus there is a limit in quantitatively measuring distribution of force or pressure.
In addition, conventionally, a zero potential method (a ground potential method) is used to read changes of resistance in an element of a tactile sensor array, which is constructed using a resistor matrix, without interference of neighboring resistors. However, since a complex electronic circuit is needed in order to implement the zero potential method, it is difficult to integrate the electronic circuit with a small tactile sensor. Accordingly, as the tactile sensor is getting smaller and the number of arrays is increased, the number of signal lines is increased and the tactile sensor becomes further vulnerable to noises if the entire signal processing is performed outside the tactile sensor.
Therefore, it needs to develop a new sensor array which can quantitatively measure distribution of force or pressure, has flexibility and elasticity so as to be attachable to various curved surfaces, has a robust structure and chemical stability so as not to be easily damaged, and is able to preprocess a signal within a tactile sensor.